# a = 2
# s = '3'
# l = [1,2,3,4,5]
# l1 = list(1, 2, 3, 4, 5)#正规写法
#
# t = (1,2,3,4,5)
# t2 = tuple(1,2,3,4,5)
#
# s = {1,2,3,4,5}#重复写会被覆盖
# s2 = set(1,2,3,4,5)
#
# str = "  hello world  "
# print(str.strip())

str7 = 'aBcdEfg'
str7.upper()
for s in (0, len(str7)):
    if str7[s].islower():
        str7[s].upper()
    else:
        str7[s].lower()

print(str7)